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<title>Chapter 39. Boost.TypeIndex 4.1</title>
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<div><h2 class="title">
<a name="boost_typeindex"></a>Chapter 39. Boost.TypeIndex 4.1</h2></div>
<div><p class="copyright">Copyright © 2012-2025 Antony
      Polukhin</p></div>
<div><div class="legalnotice">
<a name="boost_typeindex.legal"></a><p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
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<div class="toc">
<p><b>Table of Contents</b></p>
<dl class="toc">
<dt><span class="section"><a href="boost_typeindex.html#boost_typeindex.motivation">Motivation</a></span></dt>
<dt><span class="section"><a href="boost_typeindex/getting_started.html">Getting started</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="boost_typeindex/getting_started.html#boost_typeindex.getting_started.how_to_use">How to use</a></span></dt>
<dt><span class="section"><a href="boost_typeindex/getting_started.html#boost_typeindex.getting_started.example_with_boost_any">Example
      with Boost.Any</a></span></dt>
<dt><span class="section"><a href="boost_typeindex/getting_started.html#boost_typeindex.getting_started.example_with_boost_variant">Example
      with Boost.Variant</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="boost_typeindex/config.html">Configuring and building the library</a></span></dt>
<dt><span class="section"><a href="boost_typeindex/how_it_works.html">How it works</a></span></dt>
<dt><span class="section"><a href="boost_typeindex/examples.html">Examples</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="boost_typeindex/examples.html#boost_typeindex.examples.getting_human_readable_and_mangl">Getting
      human readable and mangled type names</a></span></dt>
<dt><span class="section"><a href="boost_typeindex/examples.html#boost_typeindex.examples.storing_information_about_a_type">Storing
      information about a type in container </a></span></dt>
<dt><span class="section"><a href="boost_typeindex/examples.html#boost_typeindex.examples.getting_through_the_inheritance_">Getting
      through the inheritance to receive a real type name </a></span></dt>
<dt><span class="section"><a href="boost_typeindex/examples.html#boost_typeindex.examples.using_runtime_cast_where_rtti_is">Using
      runtime_cast where RTTI is unavailable or undesirable </a></span></dt>
<dt><span class="section"><a href="boost_typeindex/examples.html#boost_typeindex.examples.exact_type_matching_storing_type">Exact
      type matching: storing type with const, volatile and reference qualifiers</a></span></dt>
<dt><span class="section"><a href="boost_typeindex/examples.html#boost_typeindex.examples.table_of_raw_name_and_pretty_nam">Table
      of raw_name() and pretty_name() outputs with and without RTTI </a></span></dt>
<dt><span class="section"><a href="boost_typeindex/examples.html#boost_typeindex.examples.c_14_checking_namespace_at_compi">C++14:
      Checking namespace at compile time </a></span></dt>
<dt><span class="section"><a href="boost_typeindex/examples.html#boost_typeindex.examples.c_14_checking_lexigraphical_orde">C++14:
      Checking lexigraphical order of provided types </a></span></dt>
</dl></dd>
<dt><span class="section"><a href="boost_typeindex_header_reference.html">Boost.TypeIndex Header Reference</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="boost_typeindex_header_reference.html#doxygen.boost_typeindex_header_reference.type__index_8hpp">Header &lt;boost/type_index.hpp&gt;</a></span></dt>
<dt><span class="section"><a href="boost_typeindex_header_reference.html#doxygen.boost_typeindex_header_reference.ctti__type__index_8hpp">Header &lt;boost/type_index/ctti_type_index.hpp&gt;</a></span></dt>
<dt><span class="section"><a href="boost_typeindex_header_reference.html#doxygen.boost_typeindex_header_reference.runtime__cast_8hpp">Header &lt;boost/type_index/runtime_cast.hpp&gt;</a></span></dt>
<dt><span class="section"><a href="boost_typeindex_header_reference.html#doxygen.boost_typeindex_header_reference.boost__shared__ptr__cast_8hpp">Header &lt;boost/type_index/runtime_cast/boost_shared_ptr_cast.hpp&gt;</a></span></dt>
<dt><span class="section"><a href="boost_typeindex_header_reference.html#doxygen.boost_typeindex_header_reference.pointer__cast_8hpp">Header &lt;boost/type_index/runtime_cast/pointer_cast.hpp&gt;</a></span></dt>
<dt><span class="section"><a href="boost_typeindex_header_reference.html#doxygen.boost_typeindex_header_reference.reference__cast_8hpp">Header &lt;boost/type_index/runtime_cast/reference_cast.hpp&gt;</a></span></dt>
<dt><span class="section"><a href="boost_typeindex_header_reference.html#doxygen.boost_typeindex_header_reference.register__runtime__class_8hpp">Header &lt;boost/type_index/runtime_cast/register_runtime_class.hpp&gt;</a></span></dt>
<dt><span class="section"><a href="boost_typeindex_header_reference.html#doxygen.boost_typeindex_header_reference.std__shared__ptr__cast_8hpp">Header &lt;boost/type_index/runtime_cast/std_shared_ptr_cast.hpp&gt;</a></span></dt>
<dt><span class="section"><a href="boost_typeindex_header_reference.html#doxygen.boost_typeindex_header_reference.stl__type__index_8hpp">Header &lt;boost/type_index/stl_type_index.hpp&gt;</a></span></dt>
<dt><span class="section"><a href="boost_typeindex_header_reference.html#doxygen.boost_typeindex_header_reference.type__index__facade_8hpp">Header &lt;boost/type_index/type_index_facade.hpp&gt;</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="boost_typeindex/making_a_custom_type_index.html">Making a custom
    type_index</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="boost_typeindex/making_a_custom_type_index.html#boost_typeindex.making_a_custom_type_index.basics">Basics</a></span></dt>
<dt><span class="section"><a href="boost_typeindex/making_a_custom_type_index.html#boost_typeindex.making_a_custom_type_index.getting_type_infos_at_runtime">Getting
      type infos at runtime</a></span></dt>
<dt><span class="section"><a href="boost_typeindex/making_a_custom_type_index.html#boost_typeindex.making_a_custom_type_index.using_new_type_infos_all_around_">Using
      new type infos all around the code</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="boost_typeindex/space_and_performance.html">Space and Performance</a></span></dt>
<dt><span class="section"><a href="boost_typeindex/code_bloat.html">Code bloat</a></span></dt>
<dt><span class="section"><a href="boost_typeindex/rtti_emulation_limitations.html">RTTI emulation
    limitations</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="boost_typeindex/rtti_emulation_limitations.html#boost_typeindex.rtti_emulation_limitations.define_the_boost_type_index_func">Define
      the BOOST_TYPE_INDEX_FUNCTION_SIGNATURE macro</a></span></dt>
<dt><span class="section"><a href="boost_typeindex/rtti_emulation_limitations.html#boost_typeindex.rtti_emulation_limitations.fixing_pretty_name_output">Fixing
      pretty_name() output</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="boost_typeindex/mixing_sources_with_rtti_on_and_.html">Mixing
    sources with RTTI on and RTTI off</a></span></dt>
<dt><span class="section"><a href="boost_typeindex/acknowledgements.html">Acknowledgements</a></span></dt>
</dl>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="boost_typeindex.motivation"></a><a class="link" href="boost_typeindex.html#boost_typeindex.motivation" title="Motivation">Motivation</a>
</h2></div></div></div>
<p>
      Sometimes getting and storing information about a type at runtime is required.
      For such cases a construction like <code class="computeroutput"><span class="special">&amp;</span><span class="keyword">typeid</span><span class="special">(</span><span class="identifier">T</span><span class="special">)</span></code> or C++11 class <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">type_index</span></code>
      is usually used, which is where problems start:
    </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          <code class="computeroutput"><span class="keyword">typeid</span><span class="special">(</span><span class="identifier">T</span><span class="special">)</span></code> and
          <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">type_index</span></code> require Run Time Type Info
          (RTTI)
        </li>
<li class="listitem">
          some implementations of <code class="computeroutput"><span class="keyword">typeid</span><span class="special">(</span><span class="identifier">T</span><span class="special">)</span></code>
          erroneously do not strip const, volatile and references from type
        </li>
<li class="listitem">
          some compilers have bugs and do not correctly compare <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">type_info</span></code>
          objects across shared libraries
        </li>
<li class="listitem">
          only a few implementations of Standard Library currently provide <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">type_index</span></code>
        </li>
<li class="listitem">
          no easy way to store type info without stripping const, volatile and references
        </li>
<li class="listitem">
          no nice and portable way to get human readable type names
        </li>
<li class="listitem">
          no way to easily make your own type info class
        </li>
</ul></div>
<p>
      Boost.TypeIndex library was designed to work around all those issues.
    </p>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
        <code class="computeroutput"><span class="identifier">T</span></code> means type here. Think
        of it as of <code class="computeroutput"><span class="identifier">T</span></code> in <code class="computeroutput"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span></code>
      </p></td></tr>
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